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Figure 3. A typical field arrangement for a spinal field<45 cm in length. The central axis is indicated by the dashed green line. The extent of the maximum radiation field is indicated by the solid green lines. The extent of the additional segment in the upper cervicothoracic region is indicated by blue lines, that in the lower lumber region by the yellow lines and the three segments added to the upper cervical region are defined by the red lines. The solid red line indicates the position of the lower limit of the three segments, the dotted lines indicate the position of the upper extent of the fields which also corresponds to the positions of the moving junctions.
